1. Field of Invention
The present invention relates to the mobile communication field, especially, Long Term Evolution (LTE) in the 3G mobile communication field, and more particularly, to a base station (eNB), a user equipment (UE) and methods thereof, which support an Evolved Multimedia Broadcast/Multicast Service (EMBMS) dedicated carrier.
2. Description of Prior Art
Multimedia Broadcast/Multicast Service (MBMS) is a new function of 3GPP R6, and also is an important function in 3GPP Long Term Evolution (LTE) systems based on Orthogonal Frequency Division Multiplexing (OFDM). It is termed as E-MBMS (Evolved-MBMS) in LTE, and is termed in general as MBMS in the present invention.
In future mobile network planning, since MBMS services will occupy a large amount of radio resources, it is common for MBMS to use a dedicated carrier in order to save the radio resources. This means that only MBMS services, rather than non-MBMS services, will be supported on the MBMS dedicated carrier.
There is no dedicated carrier scheme in 3GPP R6. Before initiation of an MBMS service, UTRAN (Universal Terrestrial Radio Access Network) adopts the FLC (Frequency Layer Convergence) technique, so that a UE (User Equipment) which is interested in the MBMS service will reselect an MBMS dedicated carrier. After the MBMS service is completed, UTRAN adopts the FLD (Frequency Layer Dispersion) technique, so that the network transmits instruction information of frequency layer dispersion and the UE disperses to another carrier (that is, a normal carrier, which supports non-MBMS services) based on the instruction information. As shown in FIG. 1B, (1) a UE originally camps on normal carrier 1, and an RNC issues an FLC instruction to the UE after initiation of an MBMS service; (2) the UE selects carrier 2 on which the MBMS service locates to receive the MBMS service; (3) after the MBMS service is completed, the RNC issues a FLD instruction to the UE on carrier 2; and (4) the UE reselects carrier 1.
Based on techniques in existing protocols, MBMS services can converge onto a certain carrier. However, there are some problems. If a non-MBMS service is to be initiated, one way is to reselect a non-MBMS carrier to provide the service, even if the service is some simple operations such as location region updating and receiving or transmitting of short messages. In this way, MBMS data is likely to be lost. Another way is to provide the service on the carrier on which the MBMS locates. This has the disadvantage that only limited non-MBMS services can be provided because the capacity of the carrier on which the MBMS locates is limited. Further, the coverage area of this carrier cannot be very large, even if the downlink transmission power is increased. This is because the uplink transmission power of UEs is limited. Thus, it cannot support large cell. In addition, MBMS services and non-MBMS services are transmitted in mixture on this carrier.
Further, in existing protocols, carriers are allocated in pair for uplink and downlink (as shown in FIG. 1A). However, an MBMS service only needs downlink data transmission. In other words, the uplink carrier is wasted.
Therefore, such technique has the following defects.
(1) Since MBMS services and non-MBMS services are mixed on the so-called dedicated carrier, the uplink is limited, and thus the coverage area of this carrier cannot be very large even if the downlink transmission power is increased;
(2) Switching and reselecting between different carriers are complex; and
(3) It is necessary to use carries in pairs.
Therefore, there is a need for a system and a method supporting an EMBMS dedicated carrier, which enable to simplify the system architecture and to meet MBMS performance requirements. Further, MBMS uses a dedicated carrier. As a result, the carrier carrying MBMS services is able to use a higher transmission power and thus has a larger coverage, leading to a lower deployment cost of the network.